Traditionally flexible pipe is utilized to transport production fluids, such as oil and/or gas and/or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location to a sea level location. Flexible pipe is generally formed as an assembly of a pipe body and one or more end fittings. The pipe body is typically formed as a composite of layered materials that form a fluid and pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses that impair the pipe's functionality over its lifetime. The pipe body is generally built up as a composite structure including metallic and polymer layers.
In many known flexible pipe designs the pipe includes one or more tensile armor layers. The primary load on such a layer is tension. In high pressure applications, such as in deep water and ultra deep water environments, the tensile armor layer experiences high tension loads from the internal pressure end cap load as well as weight. This can cause failure in the flexible pipe since such conditions are experienced over prolonged periods of time. For this reason, it is helpful if corrosion of the armor layers is prevented as such corrosion could otherwise lessen working life of the pipe.
Unbonded flexible pipe has been an enabler for deep water (less than 3,300 feet (1,005.84 meters)) and ultra deep water (greater than 3,300 feet) developments for over 15 years. The technology enabled the industry to initially produce in deep water in the early 90's and then to ultra deep waters up to around 6,500 feet (1,981.2 meters) in the late 90's. Water depths greater than 6,500 feet push the envelope where typical free-hanging riser configurations and flexible pipe in general can operate.
It is the increasing demand for oil which is causing exploration to occur at greater and greater depths where environmental factors are more extreme. In such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature which may lead to pipe blockage. For example, when transporting crude oil blockage of the internal bore of the flexible pipe can occur due to paraffin formation. As a method to overcome such problems it has, in the past, been suggested that a layer of thermal insulation should be provided around the barrier layer of a flexible pipe, the barrier layer being the layer forming the inner bore along which fluid is transported. The thermal insulation has been somewhat effective in insulating the inner bore of the pipe from external low temperature thus helping prevent blockage. Nevertheless, the insulation effects provided have been limited.
A further problem with known insulating techniques is that such insulating layers have typically been applied in the form of helically wound tapes fabricated from so-called syntactic foams. These syntactic foams often consist of a polypropylene matrix with embedded non-polymeric (e.g., glass) micro-spheres. A disadvantage with such technologies is that they involve two manufacturing processes for the insulation layer; first a stage to extrude a suitable tape and secondly the winding of the tape onto the flexible pipe body.
A still further disadvantage with known technologies using taped insulation is that the dew point of water in an annulus region between an outer shield layer and inner barrier layer is located at the inside of the outer shield layer where the temperature is relatively low. This is a problem because water vapor originating from water permeation through the inner barrier layer can freely migrate to the outer shield through the taped layer to form liquid where the temperature is lower. The thus formed liquid can then potentially cause corrosion to steel or other metal wires forming armor layers.
A still further disadvantage with known insulating technologies is that in the case of damage to the outer shield, for example during installation of flexible pipe in the field, the annulus of the flexible pipe between the shield layer and barrier layer may flood with seawater. This increases the risk of corrosion of the steel/metal armor wires which can lead to early failure of the flexible pipe.
It is an aim of embodiments of the present technology to at least partly mitigate the above-mentioned problems.
It is an aim of embodiments of the present technology to provide flexible pipe body which can be used in flexible pipe of a type able to transport production fluids and which includes a thermal insulation layer between an inner fluid retaining layer such as a barrier layer or liner and outer shield layer of the flexible pipe.
It is an aim of embodiments of the present technology to provide flexible pipe body which reduces the risk of corrosion of armor layers due to permeation of water through the inner fluid retaining layer and/or in the case of damage to an outer shield layer.
It is an aim of embodiments of the present technology to provide a riser assembly and method of manufacturing a flexible pipe able to operate in deep and ultra-deep water environments.
According to a first aspect of the present technology there is provided flexible pipe body for a flexible pipe, said pipe body comprising:
a fluid retaining layer:
at least one tensile armor layer;
at least one extruded thermal insulation layer over an outermost one of said at least one tensile armor layer; and
an outer shield layer over the insulation layer.
According to a second aspect of the present technology there is provided a method of manufacturing flexible pipe body, the method comprising:
providing a tubular fluid retaining layer;
forming at least one tensile armor layer over the fluid retaining layer:
extruding a thermally insulating layer over an outermost one of said at least one tensile armor layer; and
forming an outer shield layer over the insulating layer.
According to a third aspect of the present technology there is provided a method of providing a flexible pipe, the method comprising:
securing a respective end fitting to each of two free ends of a portion of flexible pipe body; and
during the securing step, sealing a respective end fitting to an extruded thermally insulating layer formed in the flexible pipe body between an outermost tensile armor layer and an outer shield layer thereby providing a liquid water barrier from end fitting to end fitting along the length of the flexible pipe.
According to a fourth aspect of the present technology, a method comprises:
providing a flexible pipe body comprising a fluid retaining layer, at least one tensile armor layer, at least one extruded thermal insulation layer over an outermost one of said at least one tensile armor layer, and an outer shield layer over the insulation layer; and
transporting fluid through the pipe body.
Embodiments of the present technology provide flexible pipe body in which a thermal insulation layer is extruded over an outside of an outer tensile armor layer. This forms a continuous layer along the flexible pipe body between end fittings of the flexible pipe. This insulation layer is thus sealed from end to end of the flexible pipe. On the outside of the insulation layer the outer shield layer is extruded and this provides a number of advantages. Firstly, thermal insulation is provided to reduce or eliminate blockage of the inner pipe bore by, for example, ensuring that the temperature within the barrier layer does not drop below the paraffin cloud point if crude oil is being transported. A second advantage is the prevention of convection of water vapor from transport fluid through the barrier layer or liner across the annulus to the inside surface of the outer shield where the water vapor will make the transition to liquid water due to cooler temperatures. Such water liquid might otherwise permeate back towards the bore of the pipe and potentially corrode any armor layers. Thirdly, the extruded insulation layer provides an additional barrier against liquid water ingress to a region where metallic wires may be found should an outer shield layer be accidentally breached. The need to ‘pig’ the pipeline may thus be delayed or eliminated.
The flexible pipe body can be used, for example, for the extraction, transport or refining of mineral oil or related fluids, or the transport of cold fluids, such as e.g., liquid ammonia.
The foregoing and other features and advantages of the present technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
In the drawings like reference numerals refer to like parts.